Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design; and,

FIG. 2 is a front view of a second embodiment of the display screen or portion thereof with a graphical user interface showing our new design.

The outermost broken lines illustrate a display screen or portions thereof. The remaining broken lines illustrate portions of the graphical user interface. None of the broken lines form part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 